This invention relates to electromechanical drives and in particular to the construction of apparatus comprising a combination of electronic circuitry and an electromechanical drive for use in postage franking machines.
In franking machines for printing a postal franking on mail items, settable printing elements must be set to the required value of franking prior to effecting the printing operation. Current franking machines utilise electronic circuitry for entering the desired value of franking into a register or memory and for effecting the various accounting operations which need to be carried out during use of the machine. Accordingly it is convenient to utilise electromechanical drives controlled by the electronic circuitry to physically set the mechanical printing elements to the required settings.
Stepper motors have been proposed for setting the print elements, the shaft of the stepper motor being provided with a pinion engaging with a toothed rack and the distant end of the rack having further teeth engaging a toothed wheel rotatable with a rotatable printing element. Rotation of the stepper motor through one or more steps causes the rack to be moved longitudinally and this movement of the rack results in rotational movement of the printing element.
In franking machines it is essential that at all times there is verification that the printing elements are set to the required position corresponding to the franking value entered into the machine and on which the accounting functions will be based. For this reason, means are provided to sense the setting of the printing elements and to provide control signals during resetting of the printing elements from one value to another value. Generally the franking machine must be able to print franking values represented by a number of digits and hence the machine is provided with, for example, four printing elements each individually settable.
In known constructions of franking machine, the stepper motors have been mechanically mounted on a frame member of the machine. This member also carries the mechanical components for setting and retaining the printing elements in positions corresponding to the required franking value. A printed circuit board carrying the electronic components is secured to the frame member and flying leads provide electrical connections between the stepper motors and the printed circuit board. In addition the position sensors for the printing elements are mechanically coupled to the racks and electrically connected to the printed circuit board. Such a construction has disadvantages in manufacture in that electrical connections have to be provided between what is essentially a mechanical assembly and an electronic circuit board and, if the sensors are mounted on the circuit board, it is also necessary to provide operational mechanical connections between them. This form of construction is not convenient when servicing of the machine is required.